I am putting an oil pressure gauge in my 56 F100.  Midfifty's makes a gauge and sender.  I was looking at the factory shop manual and the larger truck use a sending unit that is of similar shape.  In the shop manual they make a point of telling you that the sender must be installed with the "up" marking withing a few degrees back and forth of top center.  I notice that there are no such markings on the sender that came with my gauge.  Does anyone know why this was important on the original oil pressure sending units used with gauges back in the 50"S?

Did not know that the original sending units had a ‘TOP’ to them.  If the replacement is not marked with a ‘TOP’, then I would have to assume it makes no difference as to the orientation of the sending unit.

Lorena, Texas (South of Waco)

cokefirst, did you ask the vendor?

No, because the sender they sell does not say "top" on it.  I was just looking through the 1956 Truck shop manual and they were making a big deal about the top on the sender and the number of degrees they considered correct from exact top center.  I was more interested in the internals and why it would be so important.  I will take a photo of the page from the manual to show you the instructions.